Solidity: How to initialize an array within a struct, passed as a parameter?

Question

pragma solidity 0.4.25;

contract A{
    struct N{
        string any;
        uint256[] numberArray;
    }

    N[] public numbers;

    function init(uint256[] _numbers) public{
        for (uint256 i = 0; i < _numbers.length; i++) {
            uint256[] memory arr;
            arr[0] = _numbers[i];
            numbers.push(N("anything", arr));
        }
    }
}

This contract compiles but throws:

transact to A.init errored: VM error: invalid opcode. invalid opcode The execution might have thrown.

What I wish to achieve

Example call:

init([1,2,3,4,5])

Outcome:

N[0] = "anything", [1]

N[1] = "anything", [2]

N[2] = "anything", [3]

N[3] = "anything", [4]

N[4] = "anything", [5]

Afterwards I would like to be able to push to the array within the array.

Answer 1

I think your problem comes from the declaration of arr arry. I think you should specify the array's length.

This following code works fine:

function init(uint256[]   _numbers) public{


   for (uint256 i = 0; i < _numbers.length; i++) {

       uint256[] memory arr=new uint256[](_numbers.length);//<===as you're using only arr[0] you can use different size (exp 1).

       arr[0]= _numbers[i];
      numbers.push(N("anything", arr));
    }
}

Answer 2

I found some of the logic strange so I started breaking it down. I'm not 100% sure I solved what you want or just over-simplified it.

pragma solidity 0.4.25;

contract A{

    struct N{
        string any;
        uint[] numberArray;
    }

    N[] public numbers;

    function init(uint[] _numbers) public{
        numbers.push(N("anything", _numbers));
    }

    function getNumbersAtIndex(uint index) public view returns(uint[] _numbers) {
        return numbers[index].numberArray;
    }

}

The extra function is so you can inspect it.

At the risk of straying a little off topic, there is a risk of gas cost increase and a scaling limit. To avoid that, refactor or add functions to pass info in and get it out one element at a time.

Hope it helps.